High opacity, stencil images can be prepared by using silk screening techniques such as those described by Albert Kosloff in "The Art and Craft of Screen Process Printing," The Bruce Publishing Co., Milwaukee, Wisc. (1960). The silk screening process is, however, time consuming sometimes requiring an hour or more to prepare the final product. Additionally, silk screening is cumbersome, expensive and involves the use of solvents and thus may also involve subsequent pollution problems. A standard silk screen process requires the following steps: (1) expose the required image master on a photosensitive stencil film coated on a backing layer; (2) develop the film (wash-off solvents); (3) wash the film; (4) press the developed and washed film onto a silk screen of desired mesh size; (5) remove the film backing layer; (6) air dry the stencil on the silk screen; (7) register (6) on a substrate; (8) squeegee ink through the stenciled silk screen onto said substrate; and (9) air dry the final inked product. Although silk screening can produce a finished product with a high opacity image, the production of this high opacity requires a silk screen with a large mesh size. It is known, however, that the larger mesh size silk screens produce poorer image quality. Thus, the silk screen technique requires an operator judgment to properly balance image quality and opacity.
The use of photosensitive layers to prepare highly opaque images directly is desirable. The prior art describes other processes which directly use a photosensitive layer. These processes have certain disadvantages, however.
For example using the photosensitive compositions of U.S. Pat. No. 3,649,268, coated on a base support, exposed imagewise through an original transparency, and imaged by dusting or toning with suitable colorants (i.e., pigments), wherein the colorant adheres to the unpolymerized, tacky areas, it has not been possible to achieve high density, opaque images since sufficient pigment loading cannot be achieved. Burg et al. U.S. Pat. No. 3,060,025 teaches another imaging method whereby the colorants particles which are loosely bound on a separate support are transferred to a tacky photopolymer image by contact of the two surfaces. The Burg et al. invention is concerned with subsequent thermal transfer of the pigmented image and does not teach how to form high quality, high density, opaque images directly on the imagewise exposed photopolymer layer.